regulator: cpr-regulator: add support for per corner initial voltage fuses

A new initial voltage coding scheme has been introduced which defines
the initial voltage for each fuse corner using its own fuse value.
Previously, the initial voltage for all fuse corners was determined
from a single PVS bin fuse value. Add support in the cpr-regulator
driver for this new initial voltage coding scheme.

Each fuse encodes the initial voltage for a fuse corner as follows. The
MSB of the fuse value is a sign bit. The remaining bits define an offset.
The offset has units of a predetermined step size which is captured in
device tree. The initial voltage is then: ceiling_voltage - sign *
offset.

Change-Id: I6d48f3c68d62adc730fd406f937f7f3033b73552
Signed-off-by: Wu Fenglin <fenglinw@codeaurora.org>